After a refresh, the next refresh can be delayed by up to 60 days, after which a refresh will be performed regardless of the refresh.hold value.

We explicitly format the date command output because the version of date provided by GNU core utilities breaks RFC3339 compatibility when passing the --rfc-3339 argument. See the bug report for further details.

Use refresh.metered to pause and re-enable the refresh process when NetworkManager detects a metered connection, such as an LTE link with a limited data plan.

To hold refreshing snaps when on a metered connection:

$ sudo snap set system refresh.metered=hold

To allow refreshing:

$ sudo snap set system refresh.metered=null

By default, refresh is enabled when a metered connection is detected.

refresh.metered is available in snap 2.33 and later.

refresh.retain

Use refresh.retain to set the maximum number of a snap’s revisions stored by the system after the next refresh:

$ sudo snap set system refresh.retain=3

The refresh.retain value can be a number between 2 and 20. The default is refresh.retain=3 on Ubuntu Core systems and refresh.retain=2 on classic Ubuntu systems, such as those running Ubuntu 18.04 LTS (Bionic Beaver) and Ubuntu 16.04 LTS (Xenial Xerus).

refresh.retain is available in snap 2.34 and later.

proxy.{http,https,ftp}

These options may be set to change the proxies to be used by the system when communicating with external sites that speak the respective protocols.

Available since snapd 2.28.

service.ssh.disable

May be set to true for disabling the SSH service at startup.

Available since snapd 2.22.

system.power-key-action

Defines the behaviour of the system when the power key is pressed.

May be set to one of:

ignore

poweroff

reboot

halt

kexec

suspend

hibernate

hybrid-sleep

lock

Available since snapd 2.23.

snapshots.automatic.retention

Automatic snapshot retention time is configured with the snapshots.automatic.retention system option. The default value is 31 days, and the value needs to be greater than 24 hours: